Variable displacement internal combustion engines provide improved fuel economy and torque on demand by operating on the principle of cylinder deactivation. During operating conditions that require high output torque, every cylinder of a variable displacement internal combustion engine is supplied with fuel and air. Alternately, during operating conditions at low speed, low load, and/or other inefficient conditions for a fully displaced internal combustion engine, cylinders may be deactivated to improve the fuel economy of a vehicle equipped with the variable displacement internal combustion engine. For example, in the operation of a vehicle equipped with an eight cylinder variable displacement internal combustion engine, fuel economy will be improved if only four cylinders of the internal combustion engine are operated during relatively low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an internal combustion engine must perform to pump air from the relatively low pressure of an intake manifold, across intake and exhaust valves, and out to the atmosphere. The deactivated cylinders will disallow airflow across their respective intake and exhaust valves, thereby reducing pumping losses by forcing the internal combustion engine to operate at a higher intake manifold pressure. Since the deactivated cylinders do not allow air to flow, additional losses are avoided by operating the deactivated cylinders as “air springs” due to the compression and decompression of the air within each deactivated cylinder.
It is known in the art of engine cylinder deactivation to provide switchable hydraulic lash adjusters operable to either actuate the valves of a deactivatable cylinder or to maintain the valves in a closed position through lost motion features of the hydraulic lash adjusters. Similar mechanisms may be provided within a hydraulic valve lifter, which includes a hydraulic lash adjusting mechanism and so may be referred to broadly as a hydraulic lash adjuster.
Hydraulic lash adjusters are supplied with pressurized oil through a lash adjuster gallery or lifter oil passage to annular feed grooves, which provide oil pressure to take up the lash in the valve train between the valve tip and its associated rocker arm or other-actuator. Hydraulic lash adjusters and hydraulic valve lifters that are configured to effect cylinder deactivation typically have an additional port for a locking pin, which connects through feed passages with a valved oil pressure supply. A solenoid-actuated hydraulic control valve may be used to selectively communicate oil pressure from a main source of pressurized oil to the locking pin for cylinder deactivation. Alternately, the solenoid-actuated hydraulic control valve operates to exhaust oil pressure from the locking pin and feed passage. Traditionally, one solenoid-actuated hydraulic control valve is provided for each cylinder that is to be deactivated. Such a system is described in commonly assigned U.S. Pat. No. 6,584,951, entitled “Individual Hydraulic Circuit Modules for Engine With Hydraulically-Controlled Cylinder Deactivation”, which is hereby incorporated by reference in its entirety.